1. Field of the Invention
The present invention relates a liquid crystal display device, and more particularly, a direct type backlight assembly and a liquid crystal display device having the same.
2. Discussion of the Related Art
Cathode ray tubes (CRTs) have been widely used for monitors of TVs, measuring instruments, terminals and the like. However, the CRTs could not cope well with tendency of miniaturization and lightweight because of their weight and size. Small-sized and light liquid crystal display devices (LCDs) have been actively developed in order to replace those CRTs. The LCDs have a lot of advantages, including low power consumption.
The LCDs have large contrast ratio and are adapted for displaying gray scales or moving pictures, and also have low power consumption. The LCDs can overcome the drawbacks of the CRTs, so that they are considered as a replacement of the CRTs. However, the LCDs are a non-luminous display device, so that they require an additional external light source to irradiate light. This is because the LCDs are a light receiving device to display an image by controlling an amount of incident light, son that an additional light source (that is, a backlight assembly) for irradiating light onto an LCD panel is required.
The external light source applied to the backlight assembly can-be properly selected depending on size and use of the LCD. The external light source may be a point light source such as a light bulb and a white halogen lamp, a line light source (e.g., a hot cathode or cold cathode fluorescent lamp), or a surface light source (e.g., a light emitting diode (LED)) formed in an electroluminescent (EL) matrix from.
Also, the backlight assembly is classified into an edge type and a direct type depending upon positions of the light source with respect to a display surface. The direct type backlight assembly has high light efficiency and is easy to handle, and it has no limit in size of the display surface. For such reasons, the direct type backlight assembly has been widely used in large liquid crystal panels of 30 inches or more.
The direct type backlight assembly does not require a light guide plate that converts the line light source into the surface light source. The direct type backlight assembly includes a plurality of lamps disposed below the display surface, a reflector sheet for reflecting light emitted from the lamps, so as to prevent light loss, and a diffuser plate disposed on the lamps to scatter the light to emit uniform light.
Since a considerable space exists between the lamps and the diffuser plate, the diffuser plate is drooped due to its weight and high temperature. In order to prevent this phenomenon, a plurality of supporters are disposed between the diffuser plate and the reflector sheet. Hereinafter, a structure of a related-art direct type backlight assembly will be described with the accompanying drawings.
FIG. 1 is an expanded perspective view of a direct type backlight assembly and FIG. 2 is a cross-sectional view taken along line A-A′ of FIG. 1. Referring to FIGS. 1 and 2, the direct type backlight assembly 100 includes a plurality of lamps 101 and a bottom cover 102 where the lamps 101 are accommodated and spaced apart from one another by a predetermined distance. Also, the direct type backlight assembly 100 includes a reflector sheet 103 disposed below the lamps 101 to reflect upward the light emitted from the lamps 101, and an internal optical plate 104 disposed above the lamps 101 to reduce non-uniformity of the emitted light. The direct type backlight assembly 100 further includes a diffuser plate 105 disposed on the internal optical plate 104 to diffuse the light, and a diffuser sheet 106 disposed on the diffuser plate 105 to increase the diffusion of the light. The direct type backlight assembly 100 includes no separate light guide plate and the plurality of lamps 101 are arranged to be spaced apart by a predetermined distance.
FIG. 3 is a cross-sectional view illustrating a traveling direction of the light emitted from the lamps 101 of FIG. 1. As shown in FIG. 3, the light emitted from the lamps 101 transmits the internal optical plate 104 disposed on the lamps 101, and the distribution of light transmitting the optical plate 104 becomes uniform.
The diffuser plate 105 and the diffuser sheet 106 diffuse the light that is uniformly distributed. The internal optical plate 104 can solve the problem of the non-uniform light distribution. However, the internal optical plate 104 covers the front surface of the backlight where the lamps 101 are arranged, so that it may be distorted heat emitted from the lamps 101. Further, the use of the internal optical plate makes the backlight assembly thick.